In the operation of networks for transmission of electrical energy, natural gas, oil or the like, it is desirable to record status changes (events) of various two-state devices included in a network substation, such devices typically including circuit breakers, start-stop actuators and two-position valves. It is useful to record sequences of such changes as they occur in a substation, together with the time of occurrence of each change, for such sequence data is available for transmission to a central station, where the data is stored for subsequent correlation with sequence data from other substations. At the substation level such recorded sequence data permits an investigation of events which transpired during a major network change such as a large power outage. At the central station level, sequence data from a plurality of substations permits a study of the propagation of a change through the network.
Previously sequence of events data has been recorded automatically at unmanned substations, but the recorded data was collected manually, often necessitating trips to substation sites that are relatively inaccessible.
In some sequence of events data recorders, sequence data is stored on magnetic tape and subsequently is transmitted to a central staion through a data communication channel. Such recorders, however, perform no other function, and utilization of these recorders is costly, especially when it is desired to record data at a large number of substations each requiring its own recorder.
In a proposed data acquisition and supervisory control system for an electric power network, a remote terminal controller also records sequence of event data at its substation, but the time of an event is recorded as absolute time, which requires a real time clock and increases the size of memory for storage of sequence data.
There appears to be a need for a sequence of events recorder that records sequence data with reduced memory requirement, and without costly means for measuring the time of occurrence of a detected event. Such a recorder is desirably adapted for inclusion in a data acquisition and supervisory control system, whereby the cost of sequence data collection is reduced. In such a recorder it is further advantageous to record sequence data at a substation and to transmit wuch data to a master station in a manner that reduces the amount of time required of the master station to retrieve and process sequence data from a remote station, whereby the time available to the master to perform other functions correspondingly is increased.
The description of prior art herein is made on good faith and no representation is made that any prior art considered is the best pertaining prior art nor that the interpretation placed on it is unrebuttable.